Semiconductor wafer coatings are produced by deposition from chemical vapors, oxidation and other processes and are modified by oxidation and thermal treatment to form integrated circuits and other electronic products. These processes are performed in the reaction chambers of furnaces, the reaction chambers being formed by one or more walls of inert materials such as highly pure quartz. The wafers are positioned within a reaction chamber of the furnace during operation of the semiconductor manufacturing processes.
One of these types of furnaces is a vertical reactor such as shown in U.S. Pat. Nos. 5,320,680 and 5,618,351, the entire contents of which are hereby incorporated by reference. For purposes of clarity of explanation, the embodiment of the glassware described in this application is for a vertical reactor, although many aspects of the invention have utility in horizontal and other types of reaction furnaces, and the inventions is not limited to the vertical furnace glassware. In this application, references made to upward and downward directions relating to the glassware components and assembly are made in reference with the glassware components assembled along a vertical axis in the ultimate operating orientation of the glassware in a vertical reactor, and are intended to apply to the glassware construction in any orientation including both vertical and horizontal orientations.
In vertical furnaces, the reaction chamber can defined by a pair of concentric tubes or cylinders of quartz or other inert material which will retain their structural integrity at the elevated temperatures required for the reaction to take place in the furnace.
The double wall construction of the prior art devices present a serious cleaning problem. The internal glassware becomes coated with deposition chemicals during use, risking contamination from the coating materials, particularly when the coating fragments during repeated heating and cooling cycles. It is thus necessary to remove and clean the internal glassware from time to time. The coatings are removed by solubilizing them in chemical cleaning baths, and after the chemical solutions are removed, the residual chemicals are removed by rinsing in deionized water. Complete removal of the chemical solutions and the rinse water is required before the glassware can be reused. With double wall structures, removal of the liquid residues following chemical bath treatment and rinsing is difficult, particularly at the wall junctures. Drying the glassware in heated ovens or for prolonged periods in the atmosphere are required with the prior art devices. Furthermore, any condensates forming in the glassware tubes during lower temperature cycling operation is trapped, impairing continued use of the glassware and threatening contamination of wafers during successive operations.
Production of a unitary double wall construction of quartz tubes has been limited because of structural problems arising from the assembly and operation of the products. To provide for liquid drainage, prior art devices have been fabricated with non-concentric, off-axis constructions to provide sloped drainage surfaces. The constructions require manual assembly and welding of stationary components, yielding uneven welds with uneven wall thicknesses. At the point where the components are joined, differential cooling and contraction causes stress fractures during the cooling and before the stresses in the juncture could be relieved by annealing. Gas distribution tubes were generally vertically aligned because they did not have the structural integrity to resist bending or other structural distortions under gravity forces in elevated furnace temperatures, requiring the use of multiple tubes for reaction gas injections from multiple points in the chamber.
Sloped drainage surface glassware of this configuration required hand welding of all parts, yielding irregular joints and uneven welds which greatly reduce the structural integrity of the product and are points of fracture in the cycling heating and cooling environment of the thermal processors. Lathe welding of the off-axis components was not possible with their construction because lathe joining operations require a constant radius, co-axial construction for the components being joined on the lathe.